The decay of wood and other cellulosic materials by fungi, and the consumption of wood by termites, cause significant economic loss. Until recently, the most widely used wood preservative has been chromated copper arsenate (CCA). However, production of CCA for use in residential structures was prohibited as of January 2004 due to issues raised concerning the environmental impact and safety of arsenic and chromium used in CCA-treated lumber. As CCA replacements, arsenic-free and chromium-free wood preservatives are sought. Retention in treated wood of copper and other metal ions that are effective fungicides is a challenge. Metal salts are generally water soluble and rapidly leach from treated wood, which causes loss of the preservative function.
The decay resistance of the Western Red Cedar and other cupressaceous trees is related to the natural compound beta-thujaplicin, also known as hinokitiol. This is a natural tropolone that has fungicidal and insecticidal activities. Tropolones have been found to be effective against both brown-rot fungi and white-rot fungi [Baya et al, (2001) Pest Management Sci. v 57 p833-838].
JP 01/038,203 discloses surface wood-preserving stain treatments with main components of citronellol, trimethyl naphthalene, and oil extracted from Aomori Prefecture-grown white cedar. The white cedar oil contains the natural tropolones hinokitiol and beta-dolabrin. Copper sulfate may also be included.
JP 10/291,205 discloses an insect-repellant and decay-preventing coating for wood that is a polymer film formed by mixing solutions of sodium silicate, alum, boric acid, and tropolone solution extracted from Japanese cypress and white cedar.
JP 49/055,829 discloses the use of tropolone or Zn, Mg, Mn, Ca or Ba salts of tropolone, as an insecticidal compound when dissolved in methanol, combined with an emulsifier, and used as a wood soak.
JP 1997/175,916, JP 2001/310,302, JP 2003/3480 and JP 2004/043,327 all disclose wood preservatives containing tropolones. The disclosed wood preservatives may include other compounds, and use various means of forming the tropolonid solutions such as using different organic solvents, using different surfactants to create emulsions, and using different oils.
The flammability and/or toxicity of methanol and other organic solvents make wood preservative solutions containing these substances dangerous for manufacture and use. Requirements for recovery of, for example, methanol after any wood treatment process make preservatives based on methanol uneconomical.
There thus remains a problem in providing a highly water soluble wood preservative solution containing tropolone that is safe to use, that can penetrate wood, and yet be fixed in the wood to provide long-term protection.